﻿<%@ WebHandler Language="C#" Class="WaterMark" %>   
  
using System;   
using System.Web;   
using System.Drawing;   
using System.Drawing.Drawing2D;   
using System.Web.SessionState;     
  
public class WaterMark : IHttpHandler, IRequiresSessionState
{    // 要使用session必须实现该接口,记得要导入System.Web.SessionState命名空间     
    public void ProcessRequest(HttpContext context)   
    {   
        string checkCode = GenCode(5);  // 产生5位随机字符   
        context.Session["system_verifyCode"] = checkCode; //将字符串保存到Session中，以便需要时进行验证   
        System.Drawing.Bitmap image = new System.Drawing.Bitmap(70, 22);   
        Graphics g = Graphics.FromImage(image);   
        try  
        {   
            //生成随机生成器   
            Random random = new Random();   
  
            //清空图片背景色   
            g.Clear(Color.White);   
  
            // 画图片的背景噪音线   
            int i;   
            for (i = 0; i < 25; i++)   
            {   
                int x1 = random.Next(image.Width);   
                int x2 = random.Next(image.Width);   
                int y1 = random.Next(image.Height);   
                int y2 = random.Next(image.Height);   
                g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);   
            }   
  
            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold));   
            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2F, true);   
            g.DrawString(checkCode, font, brush, 2, 2);   
  
            //画图片的前景噪音点   
            g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);   
            System.IO.MemoryStream ms = new System.IO.MemoryStream();   
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);   
            context.Response.ClearContent();   
            context.Response.ContentType = "image/Gif";   
            context.Response.BinaryWrite(ms.ToArray());   
        }   
        finally  
        {   
            g.Dispose();   
            image.Dispose();   
        }   
    }   
  
    /// <summary>   
    /// 产生随机字符串   
    /// </summary>   
    /// <param name="num">随机出几个字符</param>   
    /// <returns>随机出的字符串</returns>   
    private string GenCode(int num)   
    {   
        string str = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        char[] chastr = str.ToCharArray();   
        string code = "";   
        Random rd = new Random();   
        int i;   
        for (i = 0; i < num; i++)   
        {   
            //code += source[rd.Next(0, source.Length)];   
            code += str.Substring(rd.Next(0, str.Length), 1);   
        }   
        return code;     
    }   
  
    public bool IsReusable   
    {   
        get  
        {   
            return false;   
        }   
    }   
  
}